The following invention relates to a paper thickness sensor in a printer.
More particularly, though not exclusively, the invention relates to a paper thickness sensor used for adjusting the space between a printhead and a platen in an A4 pagewidth drop on demand printer capable of printing up to 1600 dpi photographic quality at up to 160 pages per minute.
The overall design of a printer in which the paper thickness sensor can be utilized revolves around the use of replaceable printhead modules in an array approximately 8 inches (20 cm) long. An advantage of such a system is the ability to easily remove and replace any defective modules in a printhead array. This would eliminate having to scrap an entire printhead if only one chip is defective.
A printhead module in such a printer can be comprised of a xe2x80x9cMemjetxe2x80x9d chip, being a chip having mounted thereon a vast number of thermo-actuators in micro-mechanics and micro-electromechanical systems (MEMS). Such actuators might be those as disclosed in U.S. Pat. No. 6,044,646 to the present applicant, however, there might be other MEMS print chips.
The printhead, being the environment within which the paper thickness sensor of the present invention is to be situated, might typically have six ink chambers and be capable of printing four color process (CMYK) as well as infra-red ink and fixative. An air pump would supply filtered air to the printhead, which could be used to keep foreign particles away from its ink nozzles. The printhead module is typically to be connected to a replaceable cassette which contains the ink supply and an air filter.
Each printhead module receives ink via a distribution molding that transfers the ink. Typically, ten modules butt together to form a complete eight inch printhead assembly suitable for printing A4 paper without the need for scanning movement of the printhead across the paper width.
The printheads themselves are modular, so complete eight inch printhead arrays can be configured to form printheads of arbitrary width.
Additionally, a second printhead assembly can be mounted on the opposite side of a paper feed path to enable double-sided high speed printing.
It is an object of the present invention to provide a paper thickness sensor in a printer.
It is another object of the present invention to provide a paper thickness sensor used for adjusting a printhead-to-platen clearance for the pagewidth printhead assembly as broadly described herein.
It is another object of the present invention to provide a pagewidth printhead assembly having a paper thickness sensor therein to aid in adjusting a printhead-to-platen clearance.
It is yet another object of the present invention to provide a method of adjusting the clearance between a printhead and a platen in a pagewidth printhead assembly.
According to one aspect of the invention there is provided a pagewidth printer comprising:
a printhead having an array of printing nozzles thereon for printing on a print medium sheet having a first face and a second opposite face;
a platen disposed opposite the nozzles, the platen being rotatable about an axis of rotation and comprising a platen surface configured for supporting said sheet while the sheet is being printed on by the printhead, with at least part of said first face being supported on said platen surface, wherein the platen surface and nozzles are spaced from each other to accommodate the sheet therebetween;
a movable sensor element for engaging said second face of the sheet such that the position of the element is determined by the position of the second face and hence by the thickness of the sheet; and
a control mechanism configured to adjust the distance between said platen surface and said nozzles in response to said position of the sensor element.
According to another aspect of the invention there is provided a pagewidth printer having a printing condition and a non-printing condition, the printer comprising:
a printhead having an array of printing nozzles thereon for printing on a print medium sheet when in the printing condition;
a platen disposed opposite the nozzles, being rotatable about an axis of rotation, and comprising two operational zones angularly spaced from one another about said axis, wherein
one of said zones comprises a platen surface for supporting a said sheet thereon and which, when the printer is in the printing condition, is disposed opposite the printhead such that the platen surface and printhead define between them a space for accommodating the sheet, and
the other zone comprises a printhead engagement zone which, when the printer is in the non-printing condition, is disposed opposite the printhead and is configured for engaging the printhead;
a detector system configured for detecting a thickness of a said sheet when in said space; and
a control arrangement configured to rotate the platen to dispose a selected one of said zones opposite the printhead and to selectively vary said space in response to a said thickness detected by the detector system when the printer is in the printing condition and the platen surface is disposed opposite the printhead, for adapting the printer for differing sheet thicknesses.
The platen preferably comprises a further operational zone angularly spaced, about said axis, from each of said one zone and said other zone, wherein said one zone is a capping zone configured for engaging and capping the printhead when the printer is in the non-printing condition and said further zone is a blotting zone configured for blotting excess ink from the printhead.
Preferably, the platen surface is configured to support at least part of one face of a said sheet thereon, and wherein said detector system comprises a movable sensor element configured for engaging an opposite face of the sheet such that the position of the sensor element is determined by the position of said opposite face and hence by the thickness of the sheet. The detector system preferably comprises an optical sensor for sensing a position of said sensor element. preferably, the control arrangement is configured to effect relative displacement between the platen and the printhead in response to said sensed position, to vary said space.
In a preferred embodiment, the control arrangement comprises a cam fixed in rotation with the platen and a cam follower fixed relative to the printhead for engaging the cam. Preferably, the cam is configured, on rotation of the platen, to determine the position of the printhead relative to the platen so as to selectively and respectively dispose each said zone opposite the printhead, to respectively engage said other zone or said further zone with the printhead when the respective zone is disposed opposite the printhead, and to vary said space when the platen surface is opposite the printhead.
The control arrangement preferably comprises a motor configured for rotating the platen about said axis.
As used herein, the term xe2x80x9cinkxe2x80x9d is intended to mean any fluid which flows through the printhead to be delivered to a sheet. The fluid may be one of many different coloured inks, infra-red ink, a fixative or the like.